Electrolyte for copper refining, including polyvinyl alcohol



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ELECTROLYTE FOR CGPREP. REFIWING, INCLUDING PQLYVENYL ALCGHOL No Drawing. Application December 1, 1953,

Serial No. 395,622

8 Claims. (Cl. 204-408) This invention relates to the electrolytic refining of copper using an electrolyte including glue and polyvinyl alcohol, and is particularly directed to the provision of an improved combination of addition agents in the electrolyte, these addition agents including glue, which has been a conventional additive or addition agent in such electrolytes, and also polyvinyl alcohol, which has heretofore been unknown for use in this combination.

It has been found that with this combination, a relative ly small amount of the addition agents is required; and particularly, very high current efficiencies may be obtained, while still forming very high quality cathodes, i. e., cathodes which are solid and massive in character and which have -a minimum of included or occluded electrolyte impurities.

In the electrolytic refining of copper, an electric current is passed between cast anodes of copper to be refined and cathodes of pure electrolytically refined copper, both the anodes and cathodes being immersed in an electrolyte comprising an aqueous solution of cupric sulphate and sulphuric acid. Under the influence of the electric current, copper is dissolved from the anode into the electates Patent trolyte, and is deposited from the electrolyte onto the cathode in purified form. Impurities present in the .anode either dissolve in the electrolyte without being redcposited at the cathode, or accumulate in an insoluble anode mud. After the cathode deposit has built up to a substantial thickness (a quarter inch or more), the cathode is removed and melted for casting ,into marketable shapes.

Additions of so called addition agents are made to the electrolyte either continuously or from time to time during the refining operation. These addition agents usually are complex organic materials or mixtures of such materials, which serve to insure the formation of a smooth, dense cathode deposit. If no addition agent is .used, the cathode deposit grows very irregularly and develops sprouts or trees, which soon make contact with an adjacent and closely spaced anode and cause a short circut. When this occurs, no further amount of copper deposits on the cathode until the :short circuit is broken. Even if no short circuit develops, a rough cathode deposit favors entrainment or occlusion of pockets of electrolyte which cannot be washed out; and because the electrolyte in such pockets contains impurities that dissolved from the anode, it causes contamination of the cathode copper when the latter is melted.

The manner in which addition agents function to .produce a smooth and dense cathode deposit is not precisely and fully understood. Various theories have been formulated in attempting to explain the functions of addition agents in this connection. None of those theories will be set forth herein as it is deemed sufficient at this time to set forth exactly what practice is to be followed to obtain the desired results and to set forth the character of the results which are always attainable when operating in accordance with the present invention.

Glue, usually animal glue, has been used extensively in the past as an addition agent. This material gives some- Patented Nov. 6, i955 what improved results both as to the character of the cathodes produced when it is used and also as to current efliciency in respect to the operation using the same electrolyte but containing no glue. Glue has also been used in combination with various other addition agents (see, for example, the U. S. patent to Skowronski et al. No. 2,556,635, issued June 12, 1951, and also the co-pending U. S. application of Schloen et a1. Ser. No. 201,874, filed December 20, 1950, now Patent No. 2,660,555, issued November 24, 1953).

Polyvinyl alcohol alone, i. e., without glue or other addition agents, has also been proposed for use in electrolytes intended for plating operations (as distinguished from electrolytic copper refining), particularly for plating zinc and cadmium (see U. S. patent to Barrett et al. No. 2,171,842). The French counterpart of this Barrett patent, which is French Patent No. 824,277, further purports to teach the use of polyvinyl alcohol in the plating of various metals, including copper, but gives no examples of such use. Polyvinyl alcohol, however, is used without other addition agents and in plating in a much different concentration from the concentration used and/ or usable in the electrolytic refining of copper in accordance'with the present invention. In order to test the usefulness of polyvinyl alcohol as an addition agent in the electrolyte for copper refining, a test run was made wherein polyvinyl alcohol alone (i. e., without glue or other addition agent) was used. The resulting cathodes were so rough and irregular in character, and presumably would include and carry along much of the impurities designed to be eliminated by the refining operation, that these resulting cathodes were considered wholly unacceptable from a commercial point of view. Notwithstanding this result obtained from using polyvinyl alcohol alone, it has been found, in accordance with the present invention, that when polyvinyl alcohol is used in conjunction with some glue, the results are superior to those attainable by the use of any other single addition agent or any other known combination of addition agents. This is evidenced by data hereinafter given as to results of actual tests which have been made.

The tests made of the use of polyvinyl alcohol appear to demonstrate that the degree of polymerization does not seem to be of such a critical character that it need be seriously considered. This was shown by a number of similar and comparable tests made with polyvinyl alcohol having different 'viscosities, respectively inherent from different degrees of polymerization.

Turning now to the details of the equipment used in carrying on the process, and particularly that equipment which has been used in making the practical, substantially commercial tests of the subject matter of the present invention to provide data hereinafter given, the spacing, anode to cathode, in the cells is about 1.5 inches. The electrolyte composition as to its copper and sulphur acid content is about as follows:

Copper (calculated as metal)-43.7 grams per liter, and free HzSO4200 grams :per liter.

EXAMPLE I The present invention was tested in a group of cells or sections thereof wherein the electrolyte used contained glue and polyvinyl alcohol, both substantially in the preferred range, i. e., wherein there was about 0.077

. pounds of glue used per ton of copper deposited on the cathodes, and about 0.053 pound of polyvinyl alcohol used 3 per ton of copper deposited on the cathodes; the quantity of glue added per ton of electrolyte per day being about 0.0064 pound, and the quantity of polyvinyl alcohol used 011 the same basis being about 0.0043 pound. Over a period of 21.62 days, during which the average voltage across the cell group was 4.12 volts and the amperage about 20,000, the current consumed was 432,400 ampere-days or 1781 kilowatt-days. During this period, 471,032 pounds of copper was deposited on the cathodes, the cells of this group operating at a current elficiency of 96.5% and yielding 264.5 pounds of copper per kilowatt-day. This compared with a current efiiciency obtained in a more or less similar test using glue alone, of 90.0%. This figure might also be compared with the curent efficiencies obtained in accordance with the Skowronski et al. U. S. Patent No. 2,556,635 above referred to, wherein current efiiciencies only up to 91.7% were disclosed, but in most instances were lower than this figure (see col. 5 of the patent).

EXAMPLE II This example sets forth in tabular form the results of a number of tests wherein different amounts of glue and polyvinyl alcohol were added per day to the electrolyte, the amounts added being calculated over to a basis of pounds per ton of copper deposited on the cathode and also to pounds per day per ton of electrolyte in the circulation, both as included in Table I which follows:

Addition Agents Per- Glue P. v. A. cent; Test Cur. Lbs./

Effi- KWD Lbs./ Lbs/Day] Lbs./ Lb'sJDay/ ciency Ton Ton Elec- Ton Ton Elec- Cath trolyte Cathtrolyte odes odes In Table I above, tests ah inclusive illustrate the effect of using a substantially constant amount of glue with varying amounts of polyvinyl alcohol; while tests i to l inclusive illustrate the effect of holding the polyvinyl alcohol concentration substantially constant and varying the concentration of glue in the electrolyte.

From Table I above, it will be noted that the preferred tests as to current efiiciency are tests d and k. However, as polyvinyl alcohol is somewhat more expensive than glue, the conditions or relative concentrations used in test d are preferred over those of test k.

EXAMPLE III In this test, a number of different commercial types of polyvinyl alcohol having different percent hydrolysis and difierent viscosities were used, the same amount of polyvinyl alcohol being used in all instances. The potential in millivolts across an individual cell varied from 75 to 142 but averaged about 110 to 125. The copper deposited in all the tests of this example was from good to excellent, and in almost all instances was excellent. The tendency for a copper deposit having a character less than excellent was only indicated in instances where the potential across the cell was quite low and where the viscosity of the polyvinyl alcohol used was quite low. In general, however, all comercial grades of polyvinyl alcohol tested gave satisfactory comercial results, considered from the point of view of the character of the cathode deposits.

The concentration of the glue and of the polyvinyl alcohol in the electrolyte, in accordance with the present invention, is believed to be: (a) as to the glue, from about 0.0012 to about 00036 gram per liter; and (b) as to the polyvinyl alcohol, from about 0.0008 to about 0.0072 gram per liter. These figures are obtained by calculation based upon the amount of these respective materials which are added to the electrolyte in the making of a comercially usable electrolyte, considering the rate at which it is necesary to maintain the addition in order to maintain the desired concentration. In view of the extremely low concentrations of the addition agents in the electrolyte and the amount of impurities in commercial electrolytes used for this purpose, the methods of analysis available to the art are relatively inadequate to determine the concentrations of the additives by strictly analytical procedures. It is believed more satisfactory therefore, for the purposes of the present invention to describe accurately the amount of the several additives which must be added either per day per ton of electrolyte (a definite and ascertainable figure) or per ton of copper which is deposited on the cathodes (also definite and ascertainable). In view of the fact that the addition agents appear to be used up during the normal practice of the process and as the rates of addition of these agents appear to be about equal to the rate at which they are used up, these rates of addition are believed to be accurately representative of the present invention. Thus, the rate of addition of glue, considered in pounds per ton of copper deposited on the cathodes, should be from about 0.025 to about 0.08 and particularly (the preferred figure) about 0.076. Similarly, the rate of addition of polyvinyl alcohol in pounds per ton of copper deposited on the cathodes should be in the range of about 0.02 to about 0.14, and as a preferred figure, about 0.057.

From another point of view, and considering particularly the electrolyte per se, the rate of addition of glue in pounds per day per ton of electrolyte in the circulation should be in the range of about 0.002 to about 0.006, and as a preferred figure, about 0.0058; while the rate of addition of polyvinyl alcohol in the same units should be in the range of about 0.0014 to about 0.0116, and as a preferred value, about 0.0043.

While there is herein described certain prefer-red embodiments of the present invention and there has further been set forth what are presently believed to be the limits for the invention within which superior results in acoordance therewith, can and will be obtained, certain equivalents will suggest themselves to those skilled in the art from the foregoing disclosure. All such equivalents are to be considered included within the purview of the appended claims, which are to be construed validly as broadly as the state of the prior art permits.

What is claimed is:

1. An electrolyte composition for use in the commercial electrolytic refining of copper, including an aqueous solution of H280; and CuSO4, characterized in that said composition contains glue in a concentration of about .0012 to about .0036 gram per liter and polyvinyl alco- 1101 in a concentration of about .0008 to about .0072 gram per liter.

2. 'In the electrolytic refining of copper, involving passing an electric cub-rent between anodes of copper to be refined and cathodes of pure copper immersed in an electrolyte comprising an aqueous solution of cupric sulphate and sulphuric acid, the improvement which comprises adding to said electrolyte from about 0.025 to about 0.08 pound of glue and from about 0.02 to about 0.14 pound of polyvinyl alcohol for each ton of copper deposited on the cathodes.

3. The process according to claim 2, wherein the rates of supply of said glue and said polyvinyl alcohol are respectively about 0.076 and 0.057 pound per ton of copper deposited on the cathodes.

4. The process according to claim 2, wherein the rates of supply of said glue and said polyvinyl alcohol are respectively about 0.051 and 0.076 pound per ton of copper deposited on the cathodes.

5. In the electrolytic refining of copper, involving passing an electric current through a cell between anodes of copper to be refined and cathodes of pure copper immersed in an electrolyte comprising an aqueous solution of cupric sulphate and sulphuric acid, and involving a continuous circulation of the electrolyte through said cell, the improvement which comprises added to said electrolyte in the course of its circulation from about 0.002 to about 0.006 pound of glue and from about 0.0014 to about 0.0116 pound of polyvinyl alcohol, each per ton of electrolyte per day in an electrolyte circulation in which about 11 to about 13 tons of copper are deposited on the cathodes per day.

6. The process in accordance with claim 5, in which the quantity of glue added per ton of electrolyte per day 6 is about 0.0058 pound and the quantity of polyvinyl alcohol added per ton of electrolyte per day is about 0.0043 pound.

7. The process in accordance with claim 5, in which the quantity of glue added per ton of electrolyte per day is about 0.0039 pound and the quantity of polyvinyl alcohol added per ton of electrolyte per day is about 0.0058 pound.

=8. The process in accordance with claim 2, in which the glue and the polyvinyl alcohol are prepared as aqueous solutions which are substantially continuously supplied to the circulating electrolyte.

References Cited in the file of this patent UNITED STATES PATENTS 2,171,842 Barrett et a1. Sept. 5, 1939 2,556,635 Skowronski June 12, 1951 2,660,555 Schloen et a1 Nov. 24, 1953 FOREIGN PATENTS 824,277 France Nov. 3, 1937 

2. IN EHT ELECTROLYTIC REFINING OF COPPER, INVOLVING PASSING AN ELECTRIC CURRENT BETWEEN ANODES OF COPPER TO BE REFINED AND CATHODE OF PURE COPPER IMMERSED IN AN ELECTROLYTE COMPRISING AN AQUEOUS SOLUTION OF CUPRIC SULPHATE AND SULPHURIC ACID, THE IMPROVEMENT WHICH COMPRISES ADDING TO SAID ELECTROLYTE FROM ABOUT 0.025 TO ABOUT 0.08 POUND OF GLUE AND FROM ABOUT 0.02 TO ABOUT 0.14 POUND OF POLYVINYL ALCOHOL FOR EACH TON OF COPPER DEPOSITED ON THE CATHODES. 